A science blog for the masses

Baby-Making

Scoring a mate is only the first step in successful reproduction. The real challenge—and the whole point of mating, biologically-speaking—is successfully passing one’s genes on to the next generation (in other words: making babies).

To ensure some sort of reproductive success, most animals mate with as many individuals of the opposite sex as possible. For other animals, successful baby-making is a whole lot more complicated…

Some animals depend a little too much on a good pick-up line:

According to the IUCN, there are only 7,500 cheetahs left in Africa—plus 60 or so in Iran—and scientists doubt that even half of these animals are capable of reproducing successfully (thanks, in part, to some serious inbreeding). For cheetahs that are reproductively competent, baby-making is still a challenge.

Unlike other cats, female cheetahs don’t have regular estrus cycles and they rarely ovulate. Without an egg raring to go, an impromptu roll in the grass will not result in any cute little cheetah cubs. Instead, as scientists recently learned, cheetah pregnancies must be planned. And it’s the male that calls the shots, literally.

Male cheetahs produce a sound called a “stutter bark” that has an aphrodisiac-like effect on the ladies. Males stutter bark for a few days at a time, a few times a year, max. The stutter barking starts out at a fairly mellow pace on the first day and increases with intensity as the days progress. The female cheetah, who spends most of her life on her own, eventually responds to the male’s wooing by flicking her tail, rolling around in the grass and ovulating.

…Some take the phrase “no pain no gain” to a whole new level:

Sex isn’t exactly “fun” for female seed beetles, yet they mate five to ten times during their 25-30 day lifespan. Male seed beetles’ genitalia are armed with barbs and spikes that (obviously) injure their female partners. Scientists recently discovered that males with the most brutal sexual organs successfully fertilized more eggs than those with relatively wimpy genitalia. Why? Scientists don’t know for sure, but they think the longer spines may serve as a more effective anchor inside the female.

In a recent unrelated study, scientists asked a crucial question: why, why, WHY do female seed beetles mate more than once? The answer: for water. It is not clear whether female seed beetles want the water because they’re thirsty—they typically inhabit arid habitats—or because they need the water to store more sperm and therefore increase their reproductive success.

…And for some animals, successfully passing their genes on to the next generation is absolutely positively THE most important thing in the world:

The baby-making odds are stacked against male Australian redback spiders. They only live eight weeks and only 20 percent of them will actually find a female companion during their lifetime. Still, these guys take baby-making really, really seriously.

Why? The stakes are pretty high. Female redbacks can live for two years and store and use their mate’s sperm for their entire lives, passing their mate’s genes on to thousands of offspring.

A male redback spider begins his baby-making quest by inserting sperm packets into two appendages on the front of his head called “palps.” Then he finds himself a lady redback spider, who is 50 times his size (by weight). The male stands on the female’s abdomen and inserts one palp into one of her genital openings, then—using the palp as a pole—he pole-vaults himself into the female’s jaws. The female pierces the male’s abdomen and injects digestive enzymes. (In other words, she starts eating him.) The male then returns to his starting position, inserts his other palp into the female’s second genital opening and vaults himself into her mouth once again. This time, she eats him.

Is it really worth it? Evolutionarily-speaking, yes. Researchers found that males who were eaten mated twice as long and fertilized two times more eggs than the few males who are left uneaten. Plus, females who ate their mate were unlikely to mate again, meaning that the eaten male’s genes were the only male genes that female would be passing on to the next generation. In the end, even though the male dies a horrible death, he wins.